The following is an overview of Mobile IPv6 basic operation. A mobile node (MN) is always expected to be addressable at its home address, whether it is currently attached to its home link or is away from home. The “home address” is an IP address that is routeable to the mobile nodes home subnet and is assigned to the mobile node. While a mobile node is at home, packets addressed to its home address are routed to the mobile node's home link, using conventional Internet routing mechanisms.
While a mobile node is attached to some foreign link away from home, it is also addressable at one or more care-of addresses. A care-of address is an IP address associated with a mobile node that has the subnet prefix of a particular foreign link on which the mobile node can be reached. The mobile node can acquire its care-of address through conventional IPv6 mechanisms, such as stateless or stateful auto-configuration. As long as the mobile node stays in this location, packets addressed to this care-of address will be routed to the mobile node. The mobile node may also accept packets from several care-of addresses, such as when it is moving but still reachable at the previous link.
The association between a mobile node's home address and care-of address is known as a “binding” for the mobile node. While away from home, a mobile node registers its primary care-of address with a router on its home link, requesting this router to function as the “home agent” for the mobile node. The mobile node performs this binding registration by sending a “Binding Update” message to the home agent. The home agent replies to the mobile node by returning a “Binding Acknowledgement” message.
Any node communicating with a mobile node is referred to in this document as a “correspondent node” of the mobile node, and may itself be either a stationary node or a mobile node. Mobile nodes can provide information about their current location to correspondent nodes. This happens through a registration with the correspondent node and is referred to as route optimization. As a part of this procedure, a return routability test is performed in order to authorize the establishment of the binding. There are two possible modes for communications between the mobile node and a correspondent node. The first mode, bidirectional tunneling, does not require Mobile IPv6 support from the correspondent node and is available even if the mobile node has not registered its current binding with the correspondent node. Packets from the correspondent node are routed to the home agent and then tunneled to the mobile node. Packets to the correspondent node are tunneled from the mobile node to the home agent (“reverse tunneled”) and then routed normally from the home network to the correspondent node. In this mode, the home agent intercepts any IPv6 packets addressed to the mobile node's home address (or home addresses) on the home link. Each intercepted packet is tunneled to the mobile node's primary care-of address. This tunneling is performed using IPv6 encapsulation.
The second mode, “route optimization”, requires the mobile node to register its current care-of-address with the MIPv6 capable correspondent node. Packets from the correspondent node can be routed directly to the care-of address of the mobile node. When sending a packet to any IPv6 destination, the correspondent node checks its cached bindings for an entry for the packet's destination address. If a cached binding for this destination address is found, the node uses a new type of IPv6 routing header to route the packet to the mobile node by way of the care-of address indicated in this binding.
Routing packets directly to the mobile node's care-of address allows the shortest communications path to be used. It also eliminates congestion at the mobile node's home agent and home link. In addition, the impact of any possible failure of the home agent or networks on the path to or from it is reduced. When routing packets directly to the mobile node, the correspondent node sets the Destination Address in the IPv6 header to the care-of address of the mobile node. A new type of IPv6 routing header is also added to the packet to carry the desired home address. Similarly, when sending packets to the correspondent node, the mobile node sets the Source Address in the packet's IPv6 header to its current care-of addresses. The mobile node adds a new IPv6 “Home Address” destination option to carry its home address. The inclusion of home addresses in these packets makes the use of the care-of address transparent above the network layer (e.g., at the transport layer). Mobile IPv6 also provides support for multiple home agents, and a limited support for the reconfiguration of the home network. In these cases, the mobile node may not know the IP address of its own home agent, and even the home subnet prefixes may change over time.
A mechanism, known as “dynamic home agent address discovery” allows a mobile node to dynamically discover the IP address of a home agent on its home link, even when the mobile node is away from home. Mobile nodes can also learn new information about home subnet prefixes through the “mobile prefix discovery” mechanism.
There have been other proposals that rely on the IP-BTS to detect and initiate the route optimization procedure using a HoT/i/CoT/i/message sequence. However, these proposals require significantly more signaling to establish the binding update. The HoT/i/CoT/i/message sequence defined in RFC3775 is intended to operate between nodes that may not have a security relationship. This message sequence provides integrity and authenticity protection of the binding update messages.
Thus, there is a need in the art for a system that provides for an improved and more efficient system for mobile-to-mobile communication, especially in a base station routing architecture network.